The JPL update confirmed James' third alternative. The precision of the knowledge of the orientation of the rover was improved because they had many more sun pointing shots over time with which to refine the calculation.

This issue is perhaps not as straighforward as it might seem - at least to me. Those Sun images are roughly 20 pixels across, and let's assume the centroid can be measured to within 1 pixel. Since the Sun's angular diameter as seen from Mars is about .35 degrees, the position of the Sun can in theory be measured to within say .015 degrees. This is of course assuming the rover's position is know (it is), and the rovers's clock and Pancam pointing accuracy are at least as good as the measurements require.

Then, a series of measurement with the Sun near the zenith (to avoid refractive effects, which can't be that big a deal on Mars anyway) can be used to obtain the rover's pitch and roll, assuming a reasonable knowledge of its yaw. Yaw can not easily be measured this way - think of it this way, the Sun at zenith would look the same for all yaw values (assuming a level rover). Towards sunset a similar set of measurements can be used to refine yaw as even refractive effects would not affect the "sideways" position of the Sun is the sky. These new measurements would then be fed into the next cycle.

Given the in theory very accurate measurements of the Sun's centroid, I presume then that it is a greater inaccuracy of the rover's clock and/or Pancam pointing accuracy that limits the rover's attitude accuracy and hence benefits from averaging over multiple solls?

Well, a fascinating topic I think, and I'd be interested to learn more if anybody has any more information (as opposed to my speculation )

Then, a series of measurement with the Sun near the zenith (to avoid refractive effects, which can't be that big a deal on Mars anyway) can be used to obtain the rover's pitch and roll, assuming a reasonable knowledge of its yaw. Yaw can not easily be measured this way - think of it this way, the Sun at zenith would look the same for all yaw values (assuming a level rover). Airbag.

True but:A: The rover is not level.B: The sun shots are taken at a variety of times of day not just one.C: In this case we have sun shots taken over an extended period of time and the suns overall track has changed significantly (at least relative to the accuracy of the Pancam).

True but:A: The rover is not level.B: The sun shots are taken at a variety of times of day not just one.C: In this case we have sun shots taken over an extended period of time and the suns overall track has changed significantly (at least relative to the accuracy of the Pancam).

B: I suggested two sets of measurements should be sufficient. Looking at the positions of the Sun shots (using MMB's pano mode for sols 807-855), it appears the measurements fall into two clusters - one near the zenith, and the other about 20-30 degrees above the horizon, with some outliers in between.

C: This I believe is at the heart of the issue, assuming the Pancam pointing knowledge is indeed less than the Sun's measured accuracy (in pixels). This link states the pointing knowledge is 0.1 degrees, which although about a magnitude larger than my centroid accuracy estimates above, is still much less than the almost 2 degrees attitude adjustment. So I'm still puzzled why the adjustment was so large.

C: This I believe is at the heart of the issue, assuming the Pancam pointing knowledge is indeed less than the Sun's measured accuracy (in pixels). This link states the pointing knowledge is 0.1 degrees, which although about a magnitude larger than my centroid accuracy estimates above, is still much less than the almost 2 degrees attitude adjustment. So I'm still puzzled why the adjustment was so large.

Here's a useful link If I'm reading this correctly then in general 2 degree overall pointing was deemed sufficient as that is the accuracy required for ensuring that they HGA can be pointed at Earth so that the procedures used to refine the accuracy of the attitude could terminate as soon as the error was within that limit even though they have the capacity to be more accurate than that. One point that you made already that is probably worth investigating further is whether the clock timing accuracy (and whatever overall positional uncertainty there is for the location of the rover) could contribute to the error.

I'm still trying to find a paper that I read at some point last year that explained the attitude calculation and sun shot processes in even more detail than the one above, I'll post a link if I track it down.

Ah, thanks for that link - it made for fascinating reading. I guess it is the 'Sungaze" mode were were talking about then. I agree, it seems that HGA pointing needs drove the 2 degrees "is good enough" model. One of the sections mentioned that the attitude calculations go on until the "covariances converge to the 1.5 degree level"; presumably that means when subsequent estimates agree to within some function of pitch, yaw and roll that results in a delta of less than 1.5 degrees.

BTW, did you see that mention of in theory being able to use the gyros as a gyrocompass to detect heading, if only the software supported it? (as a fallback if the Pancam was no longer working).

It must have been very satisfying to have worked on this attitude/postion software and see such great results.

BTW, did you see that mention of in theory being able to use the gyros as a gyrocompass to detect heading, if only the software supported it? (as a fallback if the Pancam was no longer working).

Yeah - it's a very neat set up - it's pretty impressive that you can have a solidstate closed unit that can give you a decent compas (and general attitude) bearing solely from the motion of the planetary surface you happen to be perched on.

QUOTE (Airbag @ Jun 4 2006, 06:23 PM)

It must have been very satisfying to have worked on this attitude/postion software and see such great results.

Personally I'd have said that about almost any part of these magnificent machines but this is one of the very impressive parts.

Here is a combined Autostitch/MMBview version of the Spirit Sol 855 Navcam pan. It looks a bit odd, but the advantage is that the horizon is properly levelled. I couldn't for the life of me get Autostitch by itself to level it properly.

Here is a combined Autostitch/MMBview version of the Spirit Sol 855 Navcam pan. It looks a bit odd, but the advantage is that the horizon is properly levelled. I couldn't for the life of me get Autostitch by itself to level it properly.

Er, thanks mhoward.

I think autostitch must weight each join match equally -- so the near point errors introduced by non-panoramic images cause uncorrectable distortions in the panorama. A better scheme would be to weight points near the top of the panorama more heavily. Perhaps a user option parameter? 100 to -100? ( top to bottom weighting ?)

I think that I will end up using PT Assembler for the "final" product.

For those not aware, the rover camera images are NOT proper panorama images: The cameras do not pivot through the optical axis of the camera.

For people interested in real panoramas with a lot of depth this is an important factor.

Also also a uniform exposure and white balance is critical to a totally successful panorama. Again lacking in the rover images.

But we do what we gott'a do and work with what we have.

We go to the computer with the images we have and not the images we would like.

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